A device and a method for aligning sheets is known from EP 0 120 348 A2. The alignment of the front edges of the sheets takes place in a way wherein the sheets, which are arranged in the manner of fish scales, are then fed to the device and are fed to an alignment cylinder of the device at a conveying speed which is greater than the circumferential speed of the alignment cylinder. Front lays are arranged on the circumference of the alignment cylinder, and against which the front edges of the sheets can be placed. Because of the difference in the relative speeds of the sheets and the front lays, the front edge of each of the sheets is braked at least slightly, and the front edge of the sheet is aligned because of this. Following the alignment of the front edge of the sheet, the area of the front edge of the sheet is fixed on a suction strip on the alignment cylinder by the application of a vacuum, so that the sheet is looped around the circumference of the alignment cylinder because of the continued rotational movement of the alignment cylinder. Following the alignment of the front edge of the sheet and prior to transferring the sheet to a downstream-located device, the lateral offset of a lateral edge of the sheet is measured by a measuring device. The suction strip, on which the front edge of the sheet is fixed, is linearly displaced axially in the direction of the axis of rotation of the alignment cylinder as a function of the result of the measurement of the sheet lateral offset, in order to align the lateral edge of the sheet in accordance with a desired alignment. The result of this is that the sheet can be transferred, positioned in the correct position, with respect to its front edge, as well as to a lateral edge, to a subsequent device, such as, for example a sheet-printing press.
A device for sheet guidance in a sheet-fed rotary printing press is known from DE 23 13 150 C3. The sheets are conducted on a feed table, in scaled layers, to the device and then away from the device. The use of suction rollers, on whose entire circumferences recesses are provided, for conveying the sheets lying flat on the feed table is described. Each sheet can be fixed on the circumference of the suction roller by applying a vacuum. In this case, the suction roller is arranged in a recess of the feed table in such a way that the sheets, which lie flat on the feed table and lie tangentially against the circumference of the suction roller, can be driven. It is achieved, by this arrangement, that the respective sheets come into contact with the suction roller only in a line-shaped contact area. The driving forces are frictionally transmitted by the suction roller to each sheet only in the line-shaped contact area. Thus, no looping of the sheets around the suction rollers is required.
A device with a suction drum is known from WO 97/35795 A1. The sheets to be conveyed can be frictionally fixed to the circumference of the suction drum by the application of a vacuum. In this case, the drive mechanism of the suction drum is designed in such a way that the number of revolutions and/or the angle of rotation of the suction drum can be controlled by an independent electrical motor in accordance with pre-selected movement laws.
A sheet-feeding device for printing presses is known from DE-AS 20 46 602. The lateral offset of a lateral edge of a sheet, in relation to a desired orientation, can be detected by a measuring device. For aligning the lateral edge of the sheet, it is possible to displace an alignment cylinder, on whose circumference the sheet is fixed, axially in the direction of its axis of rotation as a function of the measurement result.
A contactless operating device for measuring the position of sheets is known from EP 0 716 287 A2. The lateral edges of the sheets can be measured by an optical system.
DE 42 39 732 A1 shows a device for aligning sheets. The sheets are initially pre-aligned by a belt system, and are thereafter finely aligned by a suction roller.
U.S. Pat. No. 5,078,384 discloses a device for aligning sheets by the use of two individually driven wheels. These driven wheels are controlled by a first sensor signalling the arrival of the sheets, and two sensors detecting the oblique position of the sheet.
EP 0 947 455 A1 describes a device for aligning sheets. Several alignment elements are actuated as a function of sensors which are arranged one behind the other.
WO 98/18053 A1 and U.S. Pat. No. 5,697,609 show devices for aligning sheets. At least three sensors are arranged one behind the other.